In recent years, the use of mobile phones, “smartphones”, laptops and tablets for wireless communication of speech and data has grown immensely such that the demands for capacity, performance and flexibility in public cellular networks for radio access has increased dramatically to meet this growth. The capacity of a cellular radio network is dependent on a range of factors such as the number and size of cells, available radio bandwidth, usage of radio resources, configuration of hardware and software, and so forth. For example, small cells may be introduced in addition to a large macro cell to increase capacity locally in limited areas with dense traffic, hence referred to as “hot spots”. However, the need for capacity in certain areas may still go beyond the limits of the radio network resulting in unwanted latency as well as dropped or denied connections in the network.
A way of off-loading a public cellular radio network is to provide access points for so-called mobile or wireless broadband and “Wifi” at certain indoor and outdoor locations such as within a building inhabited or visited by terminal users. At such a location, one or more access points with antennas can be installed which are connected to a public fixed network e.g. via modems and routers. For example, the well-known technique of Digital Subscriber Line (DSL) is often used to provide mobile broadband and Wifi to terminal users present in certain limited and well-defined locations such as, a residence, a hotel, an airport, a shopping mall, an office, a building with several apartments, to mention a few examples.
In this description, the term “local site” will be used to represent any such limited and well-defined location, either indoor or outdoor, public or private, where one or more access points with antennas can be installed for wireless Wifi or broadband access to a public network. Different radio technologies may also be used for such access points, e.g. GSM, LTE, Wifi, HSPA/WCDMA, and so forth. Further, the term “mobile terminal” will be used to represent any device or user equipment capable of radio communication with the above access point, including but not limited to mobile phones, smartphones, laptops and tablets.
When communicating over an access point installed in a local site, the users are often situated quite close to the access point antenna and relatively low transmission power is therefore usually sufficient to achieve proper signal reception, thus typically not causing much radio interference e.g. to any cellular network in the neighborhood. Unless the access point is highly deployed and/or the access point operates at frequencies that overlap with frequencies used by a macro site of the cellular network, which may potentially cause some interference. Nevertheless, high data rates can generally be achieved at fairly low costs by means of such access points and users will prefer to use a local access point, if available, instead of the cellular network for communication, thus off-loading the cellular network.
From a radio perspective, access points can provide services over both licensed and unlicensed radio bands. In case of unlicensed bands, as the network becomes more dense, high interference can be expected but certain measures can be taken in practice to mitigate the effects of such interference. This is due to the inherent concept and nature of “unlicensed” radio bands. In case of licensed bands, interference can be expected in-between closely located local site access points, as well as between the local site's access point and a macro radio. In-between local sites therefore, with densely deployed access points, interference mitigation will be needed since it is not likely that local site access points will operate on different frequencies. As for the relationship between a macro site and a local access point, they either operate on the same frequencies and thus will benefit from interference mitigation, or they operate on different frequencies separated from one another. The latter scenario is however more cumbersome, since it will require careful frequency planning, especially in the case of multi-operator deployments.
FIG. 1 illustrates a conventional arrangement in a local site 100, here illustrated as a building, having multiple access points 102 connected to a switch 104 or the like which provides a link to a public communication network 106 for transport of data packets to and from the network 106. The switch 104 could be implemented as a router, a gateway, or similar. In this example, three exemplary access points 102 are shown, each comprising an antenna 102a and a radio unit 102b having an associated digital unit, DU, which may be implemented with the switch 104 as shown or at each radio unit. Any coding and decoding of transmitted and received signals, respectively, are made in the radio units 102b according to regular procedures, e.g. depending on the radio technology used. Conversion of the signals between analog form, as received and transmitted by the antenna, and digital form, is also performed in the radio units 102b. 
In this arrangement, a radio unit with associated digital unit are required for each access point and antenna 102, 102a. The “radio unit” in this figure typically comprises a complete radio base station, e.g. a femto base station, a wifi access point or similar, which is connected to the network 106 via Ethernet, Digital Subscriber Line (DSL), Passive Optical Network (PON), etc. Further, each radio unit 102b is typically “technology-specific” in the sense that it can only handle one certain radio technology, thus allowing communication only with terminals capable of that radio technology. Even though it would be possible to use two or more different radio units 102b for each antenna to enable different radio technologies, this alternative is rather complex and costly. The switch 104 comprises digital switching functionality which is also needed at the local site 100, and it must be capable of reading and forwarding data packets between the individual radio units 102b and the network 106. The switch and DU 104 may be placed in the building's basement, in an adjacent street cabinet, or other fitting space at the site 100 and may be connected to the network 106 by means of a conventional telephone cable that has been installed for the site 100.
FIG. 2 illustrates another conventional arrangement in a local site 200 with multiple access points 202 where each antenna has a separate radio head 202a which are all connected to the same shared radio unit 202b that processes signals to/from all the antennas, thus reducing the number of radio units to one. The radio head 202a is a unit that has the function of transferring electric signals in analog form between the respective antenna element and the shared radio unit 202b. Typically, the high frequency of received radio signals is down-converted to an Intermediate Frequency (IF) by the radio head to limit the propagation losses through wires and cables before the signals reach the radio unit 202b, and vice versa.
In the variant of FIG. 2, a switch with a Digital Unit DU 204 is likewise needed that is linked to a public communication network 206 and capable of reading and forwarding data packets to and from the radio unit 202b. Further, the shared radio unit 202b may be technology-specific unless a more advanced and more costly “multi-functional” radio unit is used capable of operating according to more than one radio technology. The shared radio unit 202b may be centrally placed in the basement, a street cabinet or other fitting place at the local site 200, e.g. together with the switch and DU 204, but not too far away from the antenna and radio heads 202a to keep the propagation losses low.
However, it is a drawback that the above-described conventional arrangements and others are limiting with respect to radio technology in that each antenna and associated radio unit allow for only one radio technology at a time. Another drawback is that radio units, digital units and switches are costly components to install and maintain at local sites, and using two or more different radio units or a multi-functional radio unit to allow for different radio technologies would add further complexity and costs, as explained above. In addition, although the radio heads are technically able to support multiple operators, different operators will want to deploy their own radio units, digital units, and often also switches, anyway. Otherwise, various network/operator-specific parameters must be configured in both the radio units and the switches. Typically, multiple sets of radio units, digital units and switches are arranged for different operators in the same local site in a multi-operator scenario. Thus, if more than one radio technology and/or more than one operator are to be deployed at a local site with access points, a range of different technology and/or operator specific radio units and digital units are needed at the local site which is obviously a costly and complex solution, making the deployment of access points in local sites less attractive.
Another possibility known in the art is to avoid costly installations at the local site by placing the radio equipment in another location remote from the local site, which is shown in WO 2004/019524 A1. Here, the radio equipment is referred to as a base station, or “BTS”, which is placed in a location called “BTS Hotel” and antenna signals are transferred between the local site, called “remote node”, and the BTS Hotel in optical form in order to keep down the propagation losses. A unit called “MUX/WDM” is used both at the BTS Hotel and the remote node for multiplexing and optical conversion of the antenna signals. In the shown arrangement, it is necessary to configure a switching function at the BTS Hotel called “local hub” more or less manually to connect each BTS with the correct remote node or site. However, this manual work can be quite laborious, particularly in case the BTS Hotel would serve a great number of local sites.